/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicMesh3.h
Given an edge and vertex on that edge, returns other vertex of edge, the two opposing verts, and the two connected triangles (OppVert2Out and Tri2Out are be InvalidID for boundary edge)
void GetVtxNbrhood ( int EdgeID, int VertexID, int & OtherVertOut, int & OppVert1Out, int & OppVert2Out, int & Tri1Out, int & Tri2Out ) const